Toroidal Plasma Current Sustainment by Lower Hybrid Waves in the WT-2 Tokamak

Abstract

By injecting rf power ${P}_{\mathrm{rf}}$ near the lower hybrid frequency into an Ohmically heated plasma near the end of tokamak discharge in the WT-2, an rf-driven current-sustained plasma is produced and continues to exist during the rf injection period, the toroidal current (${I}_{p}\ensuremath{\sim}10$ kA) being generated by the lower hybrid wave only without the Ohmic power. The efficiency of rf-driven current generation is high and attains $\frac{{I}_{p}}{{P}_{\mathrm{rf}}}\ensuremath{\approx}0.9$ kA/kW at the plasma density ${n}_{e}\ensuremath{\simeq}1.4\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, with somewhat lower efficiency at higher density.